In order to use the limited frequency band more efficiently, the broadcasting method of the guadrature Modulated color Television is generally defined to transmit the synthesis Picture Signals resulted from interleaving the color signals onto the luminance signals so that the transmitted signals can be received by the Television Set and separated into the luminance signals and the color signals.
However, in the case that the above mentioned separation is imperfectly done by the color Television Set, the various phenomena deteriorating of the picture quality are supposedly shown up. For examples, the cross luminance phenomena such as all kinds of Dot interferences, the cross color phenomena such as spreading of the color signals and appearance of the rainbow patterns, and the resolution deteriorating phenomena of the luminance signals.
The following method has been commonly recognized as the one to prevent the picture quality from being deteriorated followed by the imperfect separation of the luminance signals and the color signals. That is to say, the color signal of the NTSC method color Television's synthesis picture signals is sampled by each line and by four times the sampling frequency of the color subcarrier's, and this sampled goes through to be filtered the band pass filter or the line com-filter, which has the characteristics of 180 phase reversal of the color signal in every to samples, so that the luminance signal and the color signal are separated. In the procedures of the above described, in order to prevent the resolution of the luminance signal from being deteriorated, the color signal is separated with the cascade of the band pass filter and the line com-filter.
The detail descriptions about this conventional art are given as follows using the block diagrams of FIG. 1, 2 and 3.
In the FIG. 1, which is the block diagram required in order to separate the luminance signal and the color signal using the conventional band pass filter, the synthesis picture signal as an input goes through the one sample delay devices of 11 and 12 so that it can be delayed the period of 2 samples. The delayed signal, which now has the delay of the period of 2 samples through the delay devices of 11 and 12, again goes through the one sample delay device of 13 and 14 so that the output signal "V13" can be delayed totally by the period of 4 samples. The initial synthesis picture signal "V11", which doesn't go through the delay devices 11 to 14, and the delayed signal "V13", which has the delay of the period of 4 samples, are respectively amplified through the 1/2 amplifiers of 15 and 16, so that the signals of V11/2 and V13/2 can be obtained.
The signal "V12", which has the delay of the period of 2 samples through the delay devices of 11 and 12, and the signals "1/2V11" and "V13/2", which are amplified through the 1/2 amplifiers of 15 and 16, go into the subtractor 17 as an input so that the output signal "V12-V11/2-V13/2" can be obtained after proceeding the subtraction procedures. The output of the said subtractor 17 is amplified by half time through the 1/2 amplifier 18, so that the color signal "C=1/2V12-1/4(V11+V13)" can be obtained.
The color signal "C" coming out from the said 1/2 amplifier 18, and the delayed signal "V12" gone through the said one sample delay devices of 11 and 12, go into the subtractor 19 as an input.
In the said subtractor 19, the color signal "C" is subtracted from the signal "V12", which is delayed by the period of two samples, so that the luminance signal "Y=1/2V12+1/4(V11+V12)" can be separated.
However, the method of separating the luminance signal and the color signal using the conventional art described as the above contains the problems in the case that there is any change to the horizontal direction in the synthesis picture signal, such as the cross luminance phenomena like Dot crawling, the spreading phenomena of the color signals, and the resolution deteriorating of the luminance signals.
In the FIG. 2, which is the block diagram required in order to separate the luminance signal and the color signal using the conventional line com-filter, the synthesis picture signal(CV) as an input, which is the non-delayed signal "V21", goes into respectively the delay device of 21, which delays one period of the horizontal synchronization signal, and the 1/2 amplifier of 23.
The delayed signal "V22", which was delayed by 1 H(H: a period of horizontal synchronization signal) through the said delay device of 21, goes into as an input the delay device of 22 and the subtracter of 25 and 27.
The signal delayed by 2 H through the said delay devices of 21 and 22 goes into as an input the subtracter of 25 after it was amplified by half time through the 1/2 amplifier of 24, and the signal "V21/2" amplified by 1/2 through the 1/2 amplifier of 23 goes into as an input the subtracter of 25 as well.
In the said subtracter of 25, the signal "1/2V21" non-delayed and amplified by 1/2, and the signal "1/2V23" delayed by 2 H and amplified by 1/2 are subtracted from the signal "V22" delayed by 1 H, so that the signal "V22-1/2V21-1/2V23" can be output to the 1/2 amplifier of 26.
The, next stage, said 1/2 amplifier of 26, amplifies the input signal "V22-V21/2-V23/2" by 1/2 and produces the color signal "C" of "1/2V22-1/4(V21+V23)". The said color signal(C) and the signal "V22" delayed by 1 H are used as the input signals to the subtracter of 27, and the luminance signal(Y) "1/2V22+1/4(V21+V23)" can be separated through subtracting the color signal(C) from the said signal "V22".
However, though the said described art is served to improve the resolution a little in comparison with the pre-described method of separating the luminance signal and the color signal using the band pass filter, still the overall resolution is lower than required and the problems so-called the cross luminance phenomena like hanging dot are involved with this method in the case that there is any change to the vertical direction in the synthesis picture signal.
In the attached FIG. 3, which is the block diagram required in order to separate the luminance signal and the color signal using the pre-described band pass filter and line com-filter, the color signal will be extracted by getting the synthesis picture signal(CV) passed through the band pass filter of 31 and the line com-filter of 32.
And the luminance signal can be obtained through primarily synchronizing the synthesis picture signal(CV), which get delayed by the delay of 33, with the color signal, and subtracting in the subtractor of 34 the color signal from the output signal of the delay of 33.
However, though the art, described on this time is served to improve greatly the resolution of luminance signal and has no cross color phenomena in comparison with the pre-described method of separating the luminance signal and the color signal using respectively the band pass filter and the com-filter, still the problems of having the dots are involved even with this method in the case that there is any change to the vertical or horizontal direction in the synthesis picture signal.
On the other hand, in the prior art of U.S. Pat. No. 4,864,389, the color signal is extracted by filtering the input synthesis picture signal and the delayed signal of the 1st, 2nd line of this input synthesis picture signal through the band pass filter, and then two values are compared, one of which is the value added the color signal of the one line delayed synthesis picture signal and the other added the color signal of the one and two lines delayed synthesis picture signal commonly to the color signal of the input synthesis picture signal.
From the above comparison result, using the smaller of two absolute values, the color signal is obtained by filtering through the 1 H line com-filter, and the luminance signal is obtained by subtracting the color signal from the synthesis picture signal synchronized by getting delayed. In this case, if the absolute value is lower than some assigned threshold level, the luminance signal and the color signal will be obtained by filtering through the 2 H line com-filter, but still the problems of having the dot crawling phenomena are involved even with this method, too, in the case that there is any change to the horizontal direction in the synthesis picture signal.